One issue I did have is that Cutting/Pasting large chunks of text will result in the scroll being out of sync,
Thank you for the report. I've not noticed the case. I found some other cases (such as resize event) that should be fixed.
I'm looking forward to the PR!
Sorry for late. Before making PR, I have to resolve the issue, Laggy Scrolling in Viewer #4827. Though its cause is not relevant to this implementation, such lags will more often become observed when sync-scroll is enabled.
Ooh, excellent idea about < details >.
Unfortunately, Joplin images inside don't display once the details pane is opened - maybe if it was an < img > tag, but that becomes too much work.
My temp solution to the scrolling jumps was to just add ``` code blocks and then to remove them if I did need to see the images.
Looking forward to the updates, thank you all 
Edit: I take it back - the images are showing within the < details > now in the rendered view. The issue was multiple images needing line breaks between them.
Finally, PR has been made!
Hmm, for Cutting/Pasting problem you pointed out and 'laggy scroll problem', it took me longer than expected to solve the problems. I felt like I was looking into the dark depths of Joplin. 